Recently it has been clearly demonstrated that two separable triglyceride lipase enzymes are released into mammalian plasma by heparin injection. These enzymes are thought to be involved in the removal of lipoprotein triglyceride from the plasma compartment into tissues. One of these enzymes is of hepatic origin (G-TGL) and the second is lipoprotein lipase (LPL) from extra-hepatic tissues (primarily adipose tissue and muscle). The mechanism by which heparin releases these enzymes is not understood. There is some histochemical evidence that lipolytic activity occurs along the capillary endothelium, however, no direct evidence for the localization of the enzymes on the luminal membrane of the capillary endothelial cell has yet been presented. The purpose of this project is to provide more direct evidence for the sub- cellular localization of these two lipases. The tools to be used are immunochemical. A specific antisera for each of the enzymes has been prepared. Our present goal is to establish systems which allow these to bind to the enzyme molecules in situ, using thin sections prepared from biopsies of liver, muscle and adipose tissue. These bound antibodies will then be located with a second antibody labled with ferritin which reacts with the rabbit IgG. Secondly, these antibodies will be used to develop a radio-immunoassay so that mass of enzyme can be compared to activity. This will allow a determination of the effects of activating and inhibiting substances in plasma on lipolytic rates.